MC68HC05JJ6 Datasheet, PDF (108/216 Pages) Freescale Semiconductor, Inc – General Release Specification Microcontrollers

Analog Subsystem
INV
This is a read/write bit that controls the relative polarity of the inherent
input offset voltage of the voltage comparators. This bit allows voltage
comparisons to be made with both polarities and then averaged
together by taking the sum of the two readings and then dividing by 2
(logical shift right).
The polarity of the input offset is reversed by interchanging the
internal voltage comparator inputs while also inverting the comparator
output. This interchange does not alter the action of the voltage
comparator output with respect to its port pins. That is, the output will
only go high if the voltage on the positive input (PB2 pin for
comparator 1 and PB0 pin for comparator 2) is above the voltage on
the respective negative input (PB3 pin for comparator 1 and PB1 pin
for comparator 2). This is shown schematically in Figure 8-4. This bit
is cleared by a reset of the device.
1 = Voltage comparators internally inverted
0 = Voltage comparators not internally inverted
V+
RISE
WHEN
V+
RISE
WHEN
V+ > V–
V+ > V–
V_{IO +}
COMP
–
V_{IO +}
COMP
–
V–
V–
INV = 0
INV = 1
Figure 8-4. INV Bit Action
NOTE:
The effect of changing the state of the INV bit is to only change the
polarity of the input offset voltage. It does not change the output phase
of the CPF1 or CPF2 flags with respect to the external port pins.
General Release Specification
108
Analog Subsystem
MC68HC05JJ6/MC68HC05JP6 — Rev. 3.2
Freescale Semiconductor